Graft polymers of ethylenimine onto a polyacrylic or polymethacrylic acid backbone



United States Patent GRAFT POLYMERS 0F ETHYLENIMINE ONTO A POLYACRYLIC OR POLYMETHACRYLIC ACID BACKBONE Donald J. Endsley, Clute, and Billy W. Wilson, Lake Jackson, Tex., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Sept. 6, 1963, Ser. No. 307,016

4 Claims. (Cl. 260-874) The present invention relates to water-soluble, high molecular weight, graft polymers and to a process for their preparation. More specifically, the invention concerns graft polymers of ethylenimine and polyacrylic or polymethecrylic acids. 7

The use of a number of mineral acid or organic acid initators to prepare polymers of ethlenimine in aqueous solution is known. In the prior art processes, however, water-solubility of the polymer product is generally atrained only by sacrificing molecular weight, i.e., the molecular weights of the polymer must be limited to relatively low values in order to prepare water-soluble products.

It has now been discovered that water-soluble high molecular weight polymers can be prepared by employing polyacrylic acid, hereafter PAA, polymethacrylic acid, hereafter PMA, or mixtures thereof as initiators in the polymerization of ethylenimine.

In the general method of the present invention, watersoluble PAA, PMA, or mixtures thereof, are employed as initiators for the polymerization of ethylenimine. These initiators are prepared by polymerization of the corresponding monomers, i.e., acrylic acid or methacrylic acid, to yield an aqueous polymeric solution preferably having a viscosity (when measured, as an aqueous solution containing one weight percent polymer, in a modified Ostwald viscometer at 100 F.) of from about 0.5 to 9.0 centistokes (hereafter cs.). A ratio of polymeric initiator: ethlenimine in the range of about 1:99 to 30:70, parts by Weight, is employed to prepare the water-soluble graft polymers of the present invention. For example, a graft polymer containing 1 weight percent PAA is prepared by adding 99 grams of ethylenimine to an aqueous solution of PAA containing 1 gram of PAA. The reaction product of the mixture of ethylenimine and PAA, PMA, or mixtures of PAA and PMA, is a graftpolymer characterized by recurring units which may be represented structurally as:

(lacs til aqueous solution which is heated and stirred. This aqueous solution contains from about 50 to weight percent water and is maintained at a temperature within the range of about 70 to 100 C. fora period of time sufficient to yield a water-soluble graft polymer of the desired molecular weight as determined by viscosity measurements. The reaction solution is preferably maintained at -a temperature of about to C. for a minimum time of approximately four hours and a maximum time determined by the attainment of a constant viscosity value for a water-soluble product as indicated by sampling of the reaction contents.

In the following examples and claims, the viscosities referred to, unless otherwise explained, are values in centistokes (cs.) obtained by employing a modified Ostwald viscometer to measure, at F., the viscosity of an aqueous solution containing one weight percent of polymeric material. These viscosities are employed as a convenient and accurate reflection of comparative molecular weights of the polymeric material. The molecular weights of the graft polymer will be influenced by the molecular Weight of the initiator, the concentration of the initiator in relationship to the concentration of the ethylenimine and the type of initiator, i.e. PAA or PMA or mixtures thereof.

The following examples described completely representative specific embodiments of the present invention. These examples, however, are not to be interpreted as limiting the invention other than as defined in the claims.

All parts expressed in the examples are parts by weight unless otherwise stated.

Example 1 The polyacrylic acid employed as an initiator in the later following examples was prepared according to the following procedure. A quantity of milliliters of acrylic acid 830 milliliters of water, and 20 milliliters of a 35 Weight percent hydrogen peroxide aqueous solution were introduced into a reaction vessel equipped with means for stirring and temperature control. The mixture was stirred and maintained at a temperature within the range of 55 to 60 C. for 20 hours during which time the acrylic acid polymerized to form a final polymer product having a. 1% viscosity of 3.07 cs.

Polymethacrylic acid was prepared in a similar manner and was employed in the form of an aqueous solution of polymer having a 1% viscosity of 1.40 cs.

Example 2 Ethylenimine was polymerized by employing polyacrylic acid as an initiator in the following manner. A quantity of 198 grams of ethylenimine was introduced into a reaction vessel, equipped with means for stirring and temperature control, which contained 202 grams of a one weight percent solution of polyac'rylic acid prepared as in Example 1. The contents of this flask was heated to 80 C. and maintained at that temperature for 12 hours with continuous stirring. At the end of this 12 hour period a polymeric product resulted having a one percent viscosity of 1.39 cs. The following tables show the results of polymerization of ethylenimine (hereafter EI) in accordance with the procedure of Example 2 wherein the initiator was prepared in accordance with the procedure of Example 1. In each case, the concentra tions employed were varied as indicated in the tables. The viscosity of the graft polymer product is reported The graft polymers of the present invention have valuable utility as additives for improving the wet strength of paper. The wet strength improvement resulting from TABLE I.EFFECI OF MOL. WT. OF FAA ON FINAL GRAFT POLYMER VISCOSITY 1% Viscosity PAA, PAA cone, EI 00110., Total polymer Viscosity oi 1% viscosity o! 100 F. wt. percent wt. percent product cone, graft polymer soln polymer at 100 F.

wt. percent at 25 C.

3 97 25 75 eps .850 es. 3 97 25 375 eps 1.24 cs. 3 97 25 2,175 cps. 1.89 05.

As seen in Table I, above, the employment of higher molecular weights of PAA, i.e. higher viscosity of PAA, under otherwise standard conditions results in a more viscous graft polymer. The graft polymer product, equal to 25 wt. percent based on the total polymer-water system, was water-soluble in each case.

TABLE IL-COMPARISON OF INITIATORS use of the graft polymers of the present invention is much greater than that resulting from the use of either polyacrylic acid, polymethacrylic acid or polyalkylenimine alone. The degree of wet strength improvement resulting from the use of the graft polymers of this invention is effected by: (l) the molecular weight of the polymeric In Table II, above, the comparative eifect of employing PMA and a :50 mixture of PMA and FAA is shown. The graft polymer product was water-soluble in both cases and equaled 25 weight percent of the aqueous-polymer solution.

TABLE III.EFFECT OF TOTAL POLYMER CONCENTRATION 1% viscosity Cone. 01 Cone. of Total poly- 1% polymer v of PAA PAA, wt. EI, wt. product cone. viscosity percent percent wt. percent at 100 F.

2 98 50 1.39 cs. 3 97 25 1.24 es.

The polymer product viscosity increases appreciably, as expected, when less water is employed. The above examples resulted in water-soluble graft polymer products.

1 Solid gel formed.

The polymer product becomes water-insoluble when the ratio of PAAzEI is increased to 63:37. At lower ratios, a higher polymer product viscosity is observed as the amount of initiator is increased.

initiator and (2) the concentration of polymeric initiator in the polymer.

The wet strength increases with the molecular weight (as represented by the 1% viscosity values in the laterfollowing examples) of the PAA or PMA initiator with a maximum wet strength value reached when the 1% viscosity of the initiator increases to 4.45 cs. At viscosities greater than 4.45 es. the wet strength value decreases.

The wet strength improvement also increases with increasing graft polymer product viscosity. This viscosity, in turn, increases with increasing concentration of polymeric initiator employed. The upper limit here is dietated by the necessity of retaining water-solubility in the polymer product and the maximum amount of polymeric initiator which can be employed is less than about 30 weight percent based upon the combined amount of initiator and EI employed. Similarly, the total concentration of initiator and E1 is in turn limited to about 50 tiator-BI system employed.

Example 3 A series of graft polymers were prepared from FAA and EI by the procedures of Examples 1 and 2 and the utility of these materials in improving strength characteristics of paper were tested. The procedure for preparing hand sheets of paper treated with the graft polymers followed that outlined by the Technical Association of the Pulp and Paper Industry (TAPPI) Standard T205 111-53. Wet and dry burst strengths were determined in accordance with the procedures outlined in TAPPI Standard T403 m-53. Table V, below, is a compilation of the data obtained from these tests with the burst strengths reported in terms of pounds per square inch (p.s.i.).

Percent wet burst/dry burst 73 &L& 88433462 23345 33544444 (B) From about 1 to 30 parts by weight of said polymeric initiator, in aqueous solution, said solution containin 25 to 50 weight percent water, for a Wet burst p.s.i.

ples of Percent polymer in concentrate Quest 0 0 3 0 in polymer one (the latter prepared by HCl 11 of ethylenimine), which were 1% viscosity of Percent PAA PAA at 100 F.

C$$CCCCCC0 0% 000 000"! 72 222 2225 58 445 1 Insufiicient PAA to imitate polymerization.

In Table VI, below, data are reported on sam PAA alone and PEI al initiated polymerizatio g from about similarly tested for utility as wet strength improvers. period of time suf- The results, when compared with those in Table V, above, ficient to yield a water-soluble graft polymer, said Water demonstrate the market improvement of wet strength 25 Soluble graft polymers having a one percent solution vis- When the graft polymers of the present invention are eosity at 100 F. Of from about 0.8 centistoke [0 about 4.0 centistokes.

employed.

gth of paper paper from about based on the weight of the dry of the graft polymer product of poly- References Cited by the Examiner UNITED STATES PATENTS 2,698,793

I T. G'OOLKASIAN, Assistant Examiner.

rylic acid, polyme-th- 40 viscosity at 100 F. of u-t 8.0 centistokes, which perature of from We claim: 1. A method for preparing water-soluble graft mers of ethylenimine and a polymeric initiator selected f, said polymeric initia- (A) From about 99 to parts by weight of ethylenirnine, and

L .m .m c .m m S H 3. mm m m P m .m m e mm h O 6 h e W I b .m r m mm .1 O a .1 a a m. m t h .n w PH CM .1 1 d .1 P oc f I C I y 0 C o n m n n M t wmaam a m m I1 6 m em P P l em u m MA pzT.m a 23 m4 m W0 Pd a 0 Rd 3 3 t 99 MW 11 %m mm e Pb S m1 .DS YD. .1 D E mm L ns B wo. m we y m m m n u n m n m I vm we 7 mm 1 e I m. n m LA s EA PP from the group consisting of polyac acrylic acid and mixtures thereo tor having a 1 percent solution from about 0.8 centistoke to abo comprises heating together at a tem about 70 to 100 C.; 

1. A METHOD FOR PREPARING WATER-SOLUBLE GRAFT POLYMERS OF ETHYLENIMINE AND A POLYMERIC INITIATOR SELECTED FROM THE GROUP CONSISTING OF POLYACRYLIC ACID, POLYMETHACRYLIC ACID AND MIXTURE THEREOF, SAID POLYMERIC INITIATOR HAVING A 1 PERCENT SOLUTION VISCOSITY AT 100*F. OF FROM ABOUT 0.8 CENTISTOKE TO ABOUT 8.0 CENTISTOKES WHICH COMPRISES HEATING TOGETHER AT A TEMPERATURE OF FROM ABOUT 70* TO 100*C.; (A) FROM ABOUT 99 TO 70 PARTS BY WEIGHT OF ETHYLENIMINE, AND (B) FROM ABOUT 1 TO 30 PARTS BY WEIGHT OF SAID POLYMERIC INITIATOR, IN AQUEOUS SOLUTION, SAID SOLUTION CONTAINING FROM ABOUT 25 TO 50 WEIGHT PERCENT WATER, FOR A PERIOD OF TIME SUFFICIENT TO YIELD A WATER-SOLUBLE GRAFT POLYMER, SAID WATER SOLUBLE GRAFT POLYMERS HAVING A ONE PERCENT SOLUTION VISCOSITY AT 100*F. OF FROM ABOUT 0.8 CENTISOKE TO ABOUT 4.0 CENTISTOKES. 